I think it’s largely because the flavor formulas are geared towards what humans tend to eat. Presumably someone would have to think outside of most human experience to come up with the right flavor for mouse.

Ferrets were used to hunt rabbits – let them go, they’d run down the burrows and the rabbits would flee and you had traps set at the exits and whammo. But you had to be quick or the ferrets would then start eating the trapped rabbits.

It’s a pretty easy Adobe Photoshop/Corel Painter trick, really: Put the lens part of the image on it’s own layer, paint whatever color you want (guessing black in this case), set the transparency percent for that one layer to whatever looks best to you, and you’ve got a transparent lens, while the rest of the image is unaffected. = )